This proposal describes fundamental studies in animals to optimize emergency precordial cardiac pacing. Recent research by Zoll indicates that non-invasive cardiac pacing with large precordial electrodes can be done with much less stimulation of skeletal muscle fibers and pain receptors than had been heretofore realized. Historically, research in precordial pacing was abandoned with the successful introduction of transvenous pacers. However, precordial pacing with skin-surface electrodes -- if properly optimized -- may be faster, safer, more convenient, and even lifesaving in many temporary or emergency applications. Studies are proposed, using anesthetized and unanesthetized pigs as animal models, to specify the optimum electrode location, size and design, and the optimum current duration which mimimize pain and muscle stimulation during effective precordial pacing. Preliminary studies show that a "pacing window" exists on the thorax which dictates an optimum electrode location and size. Further preliminary studies show that improved electrode design can abolish the high current density at the perimeter of conventional conductive electrodes and in turn substantially raise the total current that can be passed without discomfort. A novel electrode configuration is proposed in addition to allow either pacing or defibrillation without loss of time, as well as immediate recovery of the transchest ECG signal without electrode polarization artifact, in order to accurately identify ventricular capture during precordial pacing.